In microbial bioreactors, sparge gas needs to be applied in close proximity to the lowest impeller, preferably directly under the lowest Rushton impeller. When using single use bioreactor bags reliably getting a bottom tethered sparger mechanism close to the impeller without actually hitting the impeller is difficult. Using a bottom tethered impeller also makes fabrication/assembly of a single use bag more difficult.
The art has seen the provision of a bioreactor sparger that is concentric about, but separate from, the impeller shaft where the sparger was a series of tubes with holed drilled in them that were tethered to the bottom of the single use bioreactor bag just below the lowest Rushton impeller. This design suffers from fabrication difficulties and that the sparger structure added an element of rigidity to the bottom of the single use bioreactor bag. Having the sparger tethered to the bag meant that its position with respect to the Rushton impeller could vary.
This sparger was a system of semi-rigid plastic tubes (with small holes drilled in them) in a semi-circular shape with an additional cross bar. The sparger was parallel to the vessel bottom and the impeller shaft passed vertically through the two cross bars spanning the semi-circular tubes. The sparger was located above the impeller core which contains the coupling magnets and below the lowest Rushton impeller on the impeller shaft.
It is known that microbial cells have protective cell walls, and tend to clump together when grown in a bioreactor. Microbial cell cultures thus require high speed, shearing impellers to break apart the clumps of cells; and require large amounts of air. Microbial cultures grow and multiply approximately twenty to forty (20-40) times faster than do mammalian cell cultures. Hence, the rates of oxygen consumption in a microbial cell fermentation culture are about 20 to 40 times greater than are those rates in a mammalian culture process.
In order to sustain growth in a microbial culture, a bioreactor for use in microbial systems must be capable of supplying oxygen to the culture faster than a bioreactor used for mammalian cells, and must be capable of breaking up clumps of cells.
The art has also seen perfusion devices which are located within the bioreactor for drawing fluid out from the bioreactor cavity.
The art lacks a shaft-mounted fluid transfer device which can act to provide either sparge gas or a feed fluid below the shaft-mounted impeller blades but above the bottom surface of a flexible or disposable bioreactor container. There is also a need for a fluid transfer device for a bioreactor which may be utilized along the length of the impeller shaft, below each impeller hub mounted on the shaft. Additionally, the art lacks a shaft-mounted fluid transfer device which can alternatively function as a perfusion device for a bioreactor.